1. Field of the Invention
The present invention relates to a dome-shaped diaphragm including a dome part which is convex forward in an oscillating direction and has a neck part at an outer peripheral part thereof, and an edge part having a roll part which is convex forward in the oscillating direction and is provided in continuation to the neck part, and more particularly, to an improvement for enhancing rigidity of the edge part by increasing a rising height of the roll part without sacrificing acoustic characteristics.
2. Description of the Related Art
FIG. 1 shows a structure of a dome-shaped speaker unit in which a dome-shaped diaphragm is employed.
This speaker unit 1 includes a magnetic circuit 3, a speaker frame 5 having this magnetic circuit 3 attached to a rear part thereof, a dome-shaped diaphragm 7 having an edge 9 continuously provided at an outer peripheral part thereof, and a voice coil 12 which is wound around a voice coil bobbin 11 in a cylindrical shape.
The magnetic circuit 3 includes a yoke 15 having a center pole 15b in a cylindrical shape which is projected from a center part of a disc-shaped plate 15a, a magnet 16 in a ring-like shape which is loosely fitted to an outer periphery of the center pole 15b, and a top plate 17 in a ring-like shape which is loosely fitted to a distal end area of the center pole 15b in such a manner that the magnet 16 is interposed between the top plate 17 and the plate 15a. 
A magnetic gap 19 for disposing the voice coil 12 is formed between an inner periphery of the top plate 17 and the center pole 15b. 
The dome-shaped diaphragm 7 has a dome part 7a in a dome-like shape which is convex forward in an oscillating direction (i.e., the forward direction of sound travel when emitted from a speaker), a neck part 7b which is provided in continuation to an outer peripheral part of this dome part 7a for permitting the voice coil bobbin 11 to be fixed thereto, and the edge 9 having a roll part 9a in a curved shape which is convex forward in the oscillating direction. An inner peripheral edge of the roll part 9a is connected to the neck part 7b. 
A flange part 9b is extended from an outer peripheral part of the edge 9. This flange part 9b is fixed to an edge supporting part 5a in the front of the speaker frame 5, in a state held between the edge supporting part 5a and a ring-shaped gasket 21 which is attached to the edge supporting part 5a. 
In the related-art dome-shaped diaphragm 7, the neck part 7b is generally in a shape of a straight tube having a short length, so that a distal end of the voice coil bobbin 11 can be engaged with the neck part 7b. A connecting portion between this neck part 7b and the inner peripheral edge of the roll part 9a is formed as a bent part, as shown in FIG. 1, which is bent at an acute angle θ (Refer to JP-A-2003-32790, for example).